Various organs and passages in the body are subject to the development of stones, calculi and the like. Gallstones are a common problem at least in the United States and are the most frequent cause of gallbladder inflammation. Calculi in other parts of the biliary system are also commonplace. Similarly, stones, calculi and the like can develop throughout the renal or urinary system, not only in the ureters and distal to them, but also in the renal tubules and in the major and minor renal calyxes. The calyxes are hollow collecting structures in the kidneys, extending from the renal pelvis, the minor calyxes in particular joining the renal pyramids. For simplicity, the calyxes can be considered as ducts extending from the connecting tubules of the renal nephrons to the ureters.
Minimally invasive surgical procedures have been developed for the removal of stones, calculi and the like from the biliary and urinary systems. Such procedures avoid the performance of invasive, open surgical procedures (such as, for example, the cholecystectomy) and can instead employ percutaneous access, in which stones, calculi and the like are removed through a percutaneously inserted access sheath. Several access routes are suitable, depending upon the specific system and the particular location in the system at which the stones, calculi or the like are found. Without regard to the access route, however, percutaneous removal is usually based upon the use of either forceps or basket-tipped catheters to engage and remove the stones, calculi, and the like.
A closed, wire-tipped basket (helical or straight wire) permits entry of the stone or the like from the side of the basket, while an open ended basket allows a head-on approach to the stone or the like. Other retrievers and graspers can include forceps or can include a loop or snare for encircling the body to be removed, the loop or snare being made of, for example, round or flat wire. Flat wire has the advantage over round wire in that baskets incorporating flat wire exhibit better resistance to twisting during use. Moreover, while surgical techniques have advanced, and endoscope accessory channels of a relatively smaller diameter have been developed, efforts to reduce the diameter of round wires incorporated in stone extraction baskets have unfortunately not met with similar success. In practice, the lowest useful round wire diameter remains about 0.007 to 0.010 in. (about 0.178 to 0.254 mm). Because there is a significant amount of wasted space inside any sheath or cannula containing round or flat wires, this limit on useful wire diameter has prevented the development of useful stone extractors of small diameter, and in particular, of extractors having an outside diameter (that is, the diameter of the sheath or cannula containing the wires) below about 1.7 French (0.022 in. or 0.56 mm).
Another desirable feature of smaller retrieval devices, especially important for urological use, would be to have a device that works with a small diameter endoscope, such as an ureteroscope, that is capable of accommodating accessory instrumentation such as a laser fiber or hydraulic lithotripsy wire to break up stones or calculi for easier removal. The limited space and limited number of lumens available in the smaller scopes makes it advantageous to create devices that are capable of sharing the existing accessory channels of the endoscope without having to increase the diameter of the lumen(s) within the scope. While some small-diameter retrieval devices are capable of being introduced through a ureteroscope, the size and design of the wire precludes having an internal lumen through which accessory instrumentation, such as that for performing a lithotripsy procedure, can be introduced into the workspace of the retrieval device.